The proposed research is directed toward the elucidation of the role of Ca2 ion and a Ca2 ion binding phosphoprotein of brain in the regulation of a contractile-ATPase (neurostenin). A homogeneous, Ca2 ion binding phosphoprotein of porcine brain, which has been previously established as a Ca2 ion dependent regulator of cyclic nucleotide phosphodiesterase, has been found to potentiate the Ca2 ion-sensitivity of neurostenin contractile ATPase. Additional investigations have provided evidence of chemical, physical and functional homology between the brain Ca2 ion binding phosphoprotein, and troponin C, the Ca2 ion- sensitizing component of skeletal muscle contractile actomyosin ATPase. A detailed comparison of the brain phosphoprotein (CDR) and skeletal muscle troponin C (TN-C) with respect to chemical and physical properties (phosphate content, N-terminal amino acid, peptide map, etc.) as well as functional properties (effects on phosphodiesterase, actomyosin ATPase) will be undertaken. A Ca2 ion-sensitive neurostenin preparation will be examined as a source of an endogenous "troponin-like" regulator by treating the preparation as an analogue of skeletal muscle natural actomyosin, that is, containing the endogenous Ca2 ion - sensitizing regulator complex. The purification of the regulatory and catalytic subunits of neurostenin will be undertaken, and the purified components characterized, chemically, physically and kinetically. The effects of cAMP fluxes on neurostenin activity, and the mechanisms of such effects, will be examined in astrocvtoma (C-6) and neuroblastoma (C-1300) cell lines. The possibility of modulation of neurostenin by a phosphorylation-dephosphorylation mechanism will be studied. Finally, the preparation of antibodies of purified neurostenin subunits will be employed for the localization of the enzyme and its regulators by histochemical immunofluorescence.